Does Size Matter?

Following on our recent post about race and intelligence: one question that often comes up is where brain size fits in. Brain size does seem to vary among human populations in the same way that the distribution of intelligence does — with East Asians, for example, having bigger brains on average than whites — so it is both tempting and reasonable to conclude that the correspondence indicates a causal relationship.

This often draws the objection, however, that females have distinctly smaller brains than males, but do not show lower average intelligence within their population groups than males. So if this difference doesn’t account for differences in intelligence within groups, why should mean brain volume be responsible for IQ differences between groups?

The answer is coming into view. It appears, as many have suspected, that the difference in brain size between males and females is due to the presence of extra machinery in the male brain for processing spatial-relationship data — a feature that is independent of general intelligence.

Charles Murray comments here.

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3 Comments

  1. Kevin Kim says

    I hear the muttering among Westerners: “Asian guys buy bigger brains to compensate for something.”

    On a more serious note, I’m curious to read about why the ability to process spatial-relationship data isn’t linked with general intelligence. The word intelligence has many definitions, but isn’t one of the more widely accepted ones “problem-solving ability”? This definition may be problematic because it seems to decouple intelligence from consciousness (think: a chess program), but assuming a charitable reading of the definition, why wouldn’t the processing of spatial relationships be included inside the Venn circle of problem-solving ability?

    Posted December 6, 2011 at 12:23 pm | Permalink
  2. Malcolm says

    Good point, Kevin. Yes, I think spatial processing is a component of general intelligence. Likewise, so is verbal ability.

    Females do better in the latter than males, generally, which compensates for their spatial-processing disadvantage in terms of average intelligence.

    The point here (which Murray makes in the linked item) seems to be that the dedicated spatial-processing hardware simply takes up more cranial volume than the corresponding verbal apparatus.

    Posted December 6, 2011 at 12:29 pm | Permalink
  3. Tao says

    You won a new stalker, I mean, follower.

    Great post.

    Posted December 16, 2011 at 8:54 am | Permalink